" The slow colonization of lichen in the face of accelerated climate change – Ordimeds

The slow colonization of lichen in the face of accelerated climate change

The Antarctic carnation is one of only two plants native to the frozen continent. It is well established on many islands in the region and on the Antarctic Peninsula, in areas where the ice is not permanent. That is to say in a growing area. Antarctic Key, along with the other native plant to these territories, Antarctic grass, is increasingly demanding of space.

A recent study on the island of Signy in the South Orkney archipelago noted that between 2009 and 2019 the land cover increased more than in the previous 50 years combined. The causes were mainly two: the increase in air temperature caused by climate change and declining sea lion populations and their impact on the environment. But the green colonization of Antarctica actually begins much earlier. It begins in the world of the invisible and of lichens.

The ground that is born from the ice

Under our feet, the ground often goes unnoticed. Dirt, dust, sand and some more or less annoying insects. But in reality, the soil is alive. About one in four species on the planet lives there. One cubic meter of land the forest can contain up to 2,000 different species of invertebrates. And if we go microscopic, millions of individuals and several thousand species of bacteria live in a single gram of soil.

Of course, not all soils are the same and they have not all always been so rich in biodiversity. in the planet there are also bare floors, lifeless, like those that arise after a volcanic eruption or when the melting of a glacier uncovers previously inaccessible territory. At this time, the construction of the land begins. The mechanisms of ecology are set in motion to conquer this new piece of land.

“Colonization occurs through processes of primary succession, processes of colonization of rocks or soils where there is nothing,” he explains. Assumption of rivers, researcher at the National Museum of Natural Sciences and expert in terrestrial microbial ecosystems, especially those that develop in extreme environments, such as polar environments. “Succession consists of a series of communities where its components are replaced. Pioneer microorganisms arrive first We don’t really know how. We believe that whatever can happen happens, but only those who can live in the conditions of the place are established. These begin to modify the soil and generate nutrients through their own metabolism. The soil develops more and more until it is possible to grow mosses and lichens, and then plants.

De los Ríos is part of the rock eaters project which seeks to unravel the processes that allow life to break through on lava and rocks in areas uncovered after retreating glaciers in Antarctica and Iceland. This year they were due to travel to the frozen continent, but a COVID-19 outbreak mid-journey forced the BioHesperides ship to turn around and suspend sampling until next year.

“These colonization processes are very slow. Micro-organisms interact with minerals in rocks, degrading them and producing fractures. As a result, nutrients are released which, when the time comes, can be used by other organisms such as lichens, for example,” explains the researcher. “That is, nutrients that were trapped in the rock are generated, and if these microorganisms did not exist, they would never reach the ground.”

The quiet conquest of lichens

Himantormia lugubris it is a special lichen. This organism endemic to Antarctica is, like the rest of the planet’s lichens, a symbiosis between a fungus and photosynthetic microorganisms (such as algae and/or cyanobacteria). The fungus provides the structure and the shelter allowing the photosynthetic micro-organisms to work under optimal conditions. In return, they offer food and energy. It functions as a kind of self-sufficient greenhouse.

Himantormia lugubris has evolved in such a way that their relationship is effective only in parts of the Antarctic Peninsula and nearby islands. The conditions you need are so specific that it is one of those organisms particularly vulnerable to climate change. And it is that lichens are not exactly known for their ability to react or their speed of adaptation to changes.

In the coastal regions of Antarctica, lichens grow about one centimeter every 100 years. In drier interior regions, such as the McMurdo Valleys, they do so at a rate of one centimeter every 1000 years. The survival strategy of lichens involves collaboration between species and slowness. A recent study by the Field Museum in Chicago indicates that the photosynthetic organisms that compose them could take several hundred thousand years to adapt to a change in climatic conditions. But over the past half-century, the average temperature on the Antarctic Peninsula has risen by around 3 degrees Celsius.

“On the one hand, we are going to have greater colonization of deglaciated areas. Glaciers are retreating and they are doing it faster, especially in polar regions such as Iceland and the Antarctic Peninsula. But, on the other hand, climate change will establish species that have not developed before and will alter the diversity of areas that were pristine until now,” concludes Asunción de los Ríos. “Additionally, it will change the appearance: areas that previously looked white will appear greener and greener.”

Carnation and Antarctic grass will continue to claim new territories and other invasive plant species are likely to get in on the action. Microorganisms will continue arrange empty soil minerals to start building stable ecosystems. And lichens will continue to move slowly, but increasingly unsteadily, in an attempt to survive climate change that originates thousands of miles from their frozen habitats.

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